Fibrous composite material and process for producing the same

ABSTRACT

A fiber-composite material ( 7 ) is comprised of a yarn aggregate ( 6 ) in which yarn ( 2 A,  2 B) including at least a bundle ( 3 ) of carbon fiber and a carbon component other than carbon fiber is three-dimensionally combined and integrally formed without separation from each other; and a matrix made of Si—SiC-based materials ( 4 A,  4 B,  5 A,  5 B) filled between the yarn ( 2 A,  2 B) adjacent to each other within the yarn aggregate ( 6 ). A method of preparing fiber-composite material is comprised of the steps of: producing bundles ( 3 ) of carbon fiber by impregnating a component of powdery carbon into the bundles ( 3 ) of carbon fiber, which eventually forms a matrix shape; forming a plastic coat around the bundles ( 3 ) of carbon fiber to obtain an intermediate material; molding the intermediate material to obtain a molded product by making the intermediate material into a yarn-shape and laminating a predetermined amount of the material, or burning the molded product to obtain a burned product; holding the molded product or the burned product and Si, at 1100 to 1400° C. in an atmosphere of inert gas; and heating the molded product or the burned product and Si to a temperature from 1450 to 2500° C., to thereby impregnate Si—SiC-based material into the inside of pores of the molded product or the burned product. A light and strong composite material is provided, which has excellent shock resistance, corrosion resistance in a strong oxidation and corrosion environments, creep resistance, spalling resistance, wear resistance, a low friction coefficient and a self-restorative ability by which a defect is healed.

TECHNICAL FIELD

[0001] The present invention relates to a fiber-composite material thatcan be used as ultra-high-heat-resistant structural material, andhigh-lubricant and hard wearing material, and more particularly to amethod of preparing the fiber-composite material.

BACKGROUND ART

[0002] With rapid progress of technical innovations, the development ofspace-round-trip aircraft and space planes in the space developmentfield, high-temperature burning gas turbines in the energy field, andhigh-temperature gas furnaces and fusion reactors in the atomic energyfield is planned all around the world as the most-advanced big projectsand is being carried out.

[0003] As an energy source next to nuclear energy and solar energy,application of hydrogen energy has been researched. In the process,expensive metals and fine ceramics have been examined as vessels for thereactions. High strength and high reliability (toughness, shockresistance) as material at medium or high temperature (200 to 2000° C.),and durability that is not affected by environment (corrosionresistance, oxidation resistance, radiation resistance) are demanded onthese structural elements.

[0004] Today, as to ceramic material having excellent heat resistance,silicon nitride and silicon carbide materials are being developed as newceramics. However, these materials have a defect of brittleness as theirintrinsic property, and they are extremely fragile when given merely asmall crack and are also weak to thermal and mechanical shock.

[0005] As means for overcoming these defects inherent in ceramics,ceramics-based composite material (CMC) that is combined with continuousceramics-based fiber has been developed. Because the material has highstrength and high toughness even at high temperature, and has excellentshock resistance and excellent durability against environments, theresearch and development on the material is actively being done as themain ultra-high heat-resistant structural material chiefly in Europe andUSA.

[0006] For example, several hundred to several thousand pieces ofceramics long fiber having a diameter of about 10 μm are bundled to formfiber bundles (yarn), and the fiber bundles are arranged two or threedimensionally to form one-direction sheets (UD sheet) or various kindsof cloths. These sheets or cloths are laminated to make a preformedproduct with a predetermined shape (fiber preform) and to make a matrixwithin the preformed product by CVI method (Chemical Vapor Infiltration:Chemical-vapor impregnating method) or by inorganic-polymer-impregnationburning method, or ceramic powder is filled into the above-mentionedpreformed product by casting-molding method and then is sintered to makea matrix. Thus, ceramics-based fiber-composite material (CMC) that iscombined with fibers in a ceramic matrix has been developed by theprocess in which

[0007] As specific examples of CMC, C/C composite and SiCfiber-reinforced Si—SiC composite are known. The former is produced byforming a matrix made of carbon in the gap among carbon fibers arrangedin two-or three-dimensional direction, and the latter is produced byimpregnating Si into the molded product comprising SiC fibers and SiCparticles.

[0008] In British Patent Specification No. 1457757, the processingmethod of impregnating C/C composite with melting Si is disclosed.According to the method, the composite material that is a C/C compositeimpregnated with Si is supposed to be produced.

[0009] C/C composite has been employed in a wide scope of fields becauseof its excellent shock resistance owing to its rich toughness, of itslightness and of its excellent strength, but the composite has alimitation in being used as ultra-high heat-resistant structuralmaterial, because the composite cannot be used at high temperature inthe presence of oxygen since the composite is composed of carbon.Further, the composite has a defect of much abrasion wear when used assliding elements because of its rather low hardness and low compressionstrength.

[0010] On the other hand, SiC fiber-reinforced Si—SiC composite isexcellent in oxidation resistance, creep resistance and in spallingresistance, but the composite is easy to be scratched. Also, the SiCfiber has a problem that the fiber cannot be used as such structuralmaterial as a turbine blade that has a complex shape or a part of thinsection, because of the low shock resistance of the fiber. It is causedby that the Sic fiber is inferior in lubricating property against Si—SiCor the like, and the drawing effect between the body material and fiberis small, which leads to the inferior toughness to C/C composite.

[0011] In the composite material described in the British PatentSpecification No. 1457757, which is a C/C composite impregnated with Si,the common C/C composite that has been known is used, and the compositematerial has the structure that has a lot of fine pores in the wholebody. That is, as described in Example 1 of the British PatentSpecification No. 1457757, after carbon fiber is coated with phenolresin, the fiber is arranged in a mold, compressed and cured so that thedesired fiber direction and shape are obtained, and then the obtainedmolded product is released from the mold and is heated at 800 to 900° C.in nitrogen atmosphere to carbonize the phenol resin. Thus, C/Ccomposite, having the structure in which the fiber is orientated in onedirection and in which the fiber is laminated, is obtained.

[0012] In such C/C composite, the phenol resin is carbonized to become apart of carbon matrix, but because the rate of carbonization is about50%, the C/C composite has the structure having a lot of fine pores inthe whole body. When this C/C composite is dipped in melting Si toimpregnate Si, although the vicinity of the surface thereof is permeatedwith Si, it is impossible to make Si permeate into the whole C/Ccomposite, especially into the center part homogeneously. Therefore, theC/C composite has still the defect that is characteristic of the C/Ccomposite material and that has not yet been solved.

[0013] In addition, when the C/C composite having such structure isimpregnate with Si, the structure of carbon fiber near the surface isbroken because of being directly contacted with high temperature meltedSi. As a result, there arise a problem that the C/C composite loses itsshock resistance, strength, high lubricant property and wear resistance.

DISCLOSURE OF THE INVENTION

[0014] The present invention has been made to solve the above-mentionedproblem, and an object of the present invention is to provide acomposite material having excellent shock resistance, corrosionresistance in strong oxidation and corrosion environment, creepresistance, spalling resistance, wear resistance, low frictioncoefficient, further, lightness and strength. Additionally, the presentinvention has a self-restorative ability by which a defect is healedunder a certain condition.

[0015] The present invention provides a fiber-composite materialcomprising: a yarn aggregate in which yarn including at least a bundleof carbon fiber and a carbon component other than carbon fiber isthree-dimensionally combined and integrally formed without separationfrom each other; and a matrix made of Si—SiC-based material filledbetween the yarn adjacent to each other within the yarn aggregate.

[0016] In the present invention, preferably, the matrix has a siliconcarbide phase having grown along the surface of the yarn, the matrix hasthe silicon phase comprising silicon, and more preferably, the siliconcarbide phase has grown between the silicon phase and the yarn.

[0017] The matrix may have an inclined composition in which the contentrate of silicon becomes higher as apart from the surface of the yarn asfar. Preferably, the yarn aggregate includes a plurality of yarn arrayelements, each of the yarn elements is formed by arranging the pluralityof yarn in a substantially parallel direction and two dimensionally, andeach of the yarn array elements is laminated to form the yarn aggregate.Then, preferably, the yarn array elements adjacent to each other arestructured such that the longitudinal direction of each yarn intersectswith each other.

[0018] In the present invention, the matrices are connected to eachother within the fiber-composite material to form a three-dimensionalnetwork structure. More specifically, the matrices are arranged in asubstantially parallel direction and two-dimensionally within each ofthe yarn array elements, and the matrices having grown within each ofthe yarn array elements adjacent to each other are connected to eachother, to thereby form a three-dimensional lattice of the matrices.

[0019] According to the present invention, there is provided a method ofpreparing fiber-composite material, comprising the steps of: producingbundles of carbon fiber by impregnating a component of powdery carbonand a component of organic binder into the bundles of carbon fiber,which eventually forms a matrix shape; forming a plastic coat around thebundles of carbon fiber to obtain an intermediate material; molding theintermediate material to obtain a molded product by making theintermediate material into a yarn-shape; then, forming the intermediatematerial into a sheet if circumstances require; and laminating apredetermined amount of the material, or burning the molded product toobtain a burned product; holding the molded product or the burnedproduct and Si, at 1100 to 1400° C. in an atmosphere of inert gas; andheating the molded product or the burned product and Si to a temperaturefrom 1450 to 2500° C., to thereby impregnate Si—SiC-based material intothe inside of pores of the molded product or the burned product.

[0020] In the method, preferably, the molded product or the burnedproduct and Si are held at a temperature of from 1100 to 1400° C. undera pressure of 0.1 to 10 hPa for one or more hours, and an inert gas iscontrolled to flow in an amount of 0.1 or more normal litters (NL) per 1kg of the total weight of the molded product or the burned product andSi. Preferably, the molded product or the burned product and Si areheated to a temperature of from 1450 to 2500° C. under a pressure of 0.1to 10 hPa.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a perspective view schematically showing theconfiguration of yarn aggregate of a fiber-composite material accordingto the present invention.

[0022]FIG. 2 is cross-sectional views schematically showing themicrostructure of the main part of a fiber-composite material accordingto the present invention, in which FIG. 2(a) is a cross-sectional viewtaken along the line IIa-IIa of FIG. 1, and FIG. 2(b) is across-sectional view taken along the line IIb-IIb of FIG. 1.

[0023]FIG. 3 is an enlarged view of a part of FIG. 2(a).

[0024]FIG. 4 is a partially sectional perspective view schematicallyshowing the microstructure of the main part of a fiber-compositematerial according to another embodiment of the present invention.

[0025]FIG. 5(a) is a sectional view of fiber-composite material 11, andFIG. 5(b) is a sectional view of fiber-composite material 16.

[0026]FIG. 6 is a photograph of EPMA showing the structure of a ceramicmaterial viewed in a sectional direction to the surface layer of a testpiece of Example 1.

[0027]FIG. 7 is a photograph of a reflective electronic image by SEMshowing the structure of the ceramic material in the sectional directionof the surface layer of the test piece of Example 1.

[0028]FIG. 8 is a view illustrating the microstructures shown in FIG. 6and FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] A fiber-composite material according to the present inventioncomprises: a yarn aggregate in which yarn including at least a bundle ofcarbon fiber and a carbon component other than carbon fiber isthree-dimensionally combined and integrally formed so as not to separatefrom each other; and a matrix made of Si—SiC-based materials filledamong the yarn adjacent to each other within the yarn aggregate.

[0030] Thus, a fiber-composite material can be given toughness by usinga C/C composite as the body material, which allows the fiber-compositematerial to have excellent shock resistance, lightness, high strength,high lubricant property and wear resistance. Therefore, it is possibleto overcome the defect of low shock resistance which SiCfiber-reinforced Si—SiC composites have and to use the composites as thestructural material that has a complex shape or a part of thin section.Since the C/C composite is produced in such a way that the C/C compositehas continuous pores inside thereof, the Si—SiC based material,impregnated into the pores and formed, has a continuous structure and athree-dimensional network structure. Therefore, any cut portion hashigher wear resistance compared with the C/C composite that is the bodymaterial, and maintains lubricant property the C/C composite hasintrinsically.

[0031] By arranging the layer comprising Si—SiC-based material on thesurface, it becomes possible to give oxidation resistance, creepresistance and spalling resistance to the fiber-composite material, toimprove the low oxidation resistance a C/C composite has, and to use thefiber-composite material at high temperature even in the presence ofoxygen. Thus, the fiber-composite material can be used as an ultra-highheat resistance structural material.

[0032] Hereinbelow, the novel fiber-composite material according to thepresent invention will be described.

[0033] The material is a material of new idea, which is made by givingimprovement to the basic composition based on a so-called C/C composite.

[0034] The C/C composite produced in the following process is known.Several hundred to several ten thousand pieces, ordinarily, of carbonfiber having a diameter of about 10 μm are bundled to obtain fiberbundles (yarn), and the fiber bundles are arranged two-dimensionally toform a one-direction sheet (UD sheet) or various kinds of cloth. Thesesheets or cloths are laminated to forn a preformed product with apredetermined shape (fiber preform). A matrix made of carbon is formedwithin the preformed product by CVI method (Chemical Vapor Infiltration:Chemical-vapor impregnating method) or by inorganic-polymer-impregnationsintering method to obtain a C/C composite.

[0035] The fiber-composite material has an excellent characteristic ofmaintaining the structure of carbon fiber without damaging thestructure, which results from that the fiber-composite material isproduced by the specific method to be described below using a C/Ccomposite as a body material. As described in the above-mentionedBritish Patent Specification No. 1457757, the fiber-composite materialthat is a C/C composite impregnated with Si is known. However, becausethe structure of carbon fiber is broken in the material, the propertiesof C/C composite such as shock resistance, strength, high lubricantproperty and wear resistance is lost.

[0036] It is supposed that because the fiber-composite materialaccording to the present invention is applied with the specifictreatment in which a soft coat made from plastic such as thermal-plasticresin is formed at least around the carbon fiber bundle to obtain a softintermediate material, and the material is made to be yarn-shaped, thenthe material is formed into a sheet if circumstances require, and thesheet is laminated and subjected to hot molding, high temperature andmelting Si causes contact reaction first with carbon particles exceptfor a carbon fiber, or highly activated carbon generated by thermaldecomposition of an organic binder and/or plastic coat, and is notdirectly contacted with the carbon fiber bundles, and that the structureof carbon fiber is not damaged.

[0037] Moreover, the fiber-composite material according to the presentinvention has the microstructure filled with the matrix made ofSi—SiC-based material among the yarn that is adjacent to each other inthe yarn aggregate.

[0038] In the present invention, Si—SiC-based material is a general termfor the material that contains Si and silicon carbide as the maincomponent. In the present invention, when Si is impregnated into the C/Ccomposite or into the molded product made of the C/C composite, Sireacts mainly with the component of carbon, except for carbon fibers, orremained carbon in the composite, and is partially carbonized to grow Sia part of which is carbonized among the yarn aggregates. The matrix maycontain some intermediate phases from the silicon phase in which siliconhas almost purely remained to the almost-pure silicon carbide phase.That is, the matrix is typically composed of the silicon phase and thesilicon carbide phase, but the matrix may contain the Si—SiC coexistingphase in which the carbon content changes with gradient based on siliconbetween the silicon phase and the silicon carbide phase. Si—SiC-basedmaterial is a general term for the material in which the carbonconcentration changes from 0 mole % to 50 mole % in such Si—SiC system.

[0039] In the fiber-composite material, preferably, the matrix comprisesthe silicon carbide phase that has grown along the surface of the yarn.In this case, the strength of each of the yarn itself is furtherimproved, and the fiber-composite material is hardly damaged.

[0040] In the fiber-composite material, preferably, the matrix comprisesthe silicon phase that is made of silicon, and the silicon carbide phasehas grown between this silicon phase and the yarn. In this case, thesurface of the yarn is strengthen by the silicon carbide phase. At thesame time, the micro-dispersion of stress is further promoted becausethe central part of the matrix is composed of the silicon phase that hasa relatively low hardness.

[0041] In the fiber-composite material, preferably, the matrix has aninclined composition in which the content rate of silicon becomes higheraccording to the distance from the surface of the yarn.

[0042] In the fiber-composite material, preferably, the yarn aggregatecomprises more than one yarn array elements, each of the yarn arrayelements being formed by arranging more than one yarn two-dimensionallyin a nearly parallel direction, and each of the yarn array elementsbeing laminated. The fiber-composite material, therewith, has alaminated structure in which the yarn array elements that have aplurality of layers are laminated toward one direction.

[0043] In this case, more preferably, the direction of the length ofeach yarn, in the yarn array elements adjacent to each other, intersectseach other. The dispersion of stress is further promoted therewith. Morepreferably, the direction of the length of each yarn, in the yarn arrayelements adjacent to each other, intersects each other at right angles.

[0044] Preferably, the matrices form three-dimensional network structureby being connected with each other in the fiber-composite material. Inthis case, more preferably, the matrices are arranged, in each of theyarn array elements, two-dimensionally in a nearly parallel direction,the matrices have grown, in each of the yarn array elements adjacent toeach other, being connected with each other, and the matrices formsthree-dimensional lattice structure therewith.

[0045] The gap among the yarn adjacent to each other, may be filled withthe matrix to the level of 100%, but the gap among the yarn may bepartially filled with the matrix.

[0046] The component of carbon other than carbon fiber in the yarn is,preferably, carbon powder, and, more preferably, the carbon powder thatis made to be graphite.

[0047]FIG. 1 is a perspective view schematically showing the idea ofyarn aggregate. FIG. 2(a) is a cross-sectional view taken along the lineIIa-IIa of FIG. 1, and FIG. 2(b) is a cross-sectional view taken on lineIIb-IIb of FIG. 1. FIG. 3 is an enlarged view of a part of taken fromFIG. 2(a).

[0048] The skeleton of fiber-composite material 7 comprises the yarnaggregate 6. The yarn aggregate 6 is constructed by laminating the yarnarray elements 1A, 1B, 1C, 1D, 1E, 1F upward and downward. In each ofthe yarn array elements, each of the yarn 3 is arrangedtwo-dimensionally, and the direction of the length of each of the yarnis nearly parallel to each other. The direction of the length of each ofthe yarn, in each of the yarn array elements adjacent to each otherupward and downward, intersects at right angles. That is, the directionof the length of each of the yarn 2A in each of the yarn array elements1A, 1C, 1E is parallel to each other, and the direction of the lengththereof intersects the direction of the length, at right angles, of eachof the yarn 2B in each of the yarn array elements 1B, 1D, 1F.

[0049] Each of the yarn comprises fiber bundle 3 comprising carbon fiberand a component of carbon except carbon fiber. The yarn array elementsare laminated to form the yarn aggregate 6 that is three-dimensional andlattice shaped. Each of the yarn has become substantially ellipticalbecause of being crushed during the pressure molding process to bedescribed below.

[0050] In each of the yarn array elements 1A, 1C, 1E, the gap among theyarn adjacent to each other is filled with the matrices 8A, each of thematrices 8A runs along the surface of the yarn 2A in parallel with theyarn. In each of the yarn array elements 1B, 1D, 1F, the gap among theyarn adjacent to each other is filled with the matrices 8B, each of thematrices 8B runs along the surface of the yarn 2B in parallel with theyarn.

[0051] In this example, the matrices 8A and 8B comprise the siliconcarbide phases 4A, 4B that coat the surface of the yarn and theSi—SiC-based material phases 5A, 5B in which the rate of containedcarbon is less than in the silicon carbide phases 4A, 4B. The siliconcarbide phases may partially contain silicon. In this example, thesilicon carbide phases 4A, 4B have grown also between the yarn 2A, 2Badjacent to each other up and down.

[0052] Each of the matrices 8A, 8B runs along the surface of yarn in thelong and narrow shape, preferably, linearly, and each of the matrices 8Aand 8B intersects at right angles each other. The matrices 8A in theyarn array elements 1A, 1C, 1E and the matrices 8B in the yarn arrayelements 1B, 1D, 1F, which intersect the matrices 8A at right angles,are respectively connected in the gap part between the yarn 2A and 2B.As the result, the matrices 8A, 8B form a three-dimensional lattice as awhole.

[0053]FIG. 4 is a partially sectional perspective view of the main partof a fiber-composite material of another embodiment of the presentinvention. In this example, a silicon carbide phase does notsubstantially exist between the yarn 2A and 2B adjacent to each other upand down. In each of the yarn array elements, the matrix 8A or 8B isformed individually between the yarn 2A and 2A adjacent to each other,or between the yarn 2B and 2B adjacent to each other. The shapes of thematrices 8A and 8B are the same as the examples of FIG. 1 to FIG. 3except that a silicon carbide phase does not exist between the yarnadjacent to each other up and down. Each of the matrices 8A and 8Bindividually comprises the silicon carbide phase 5C, that has grown incontact with the surfaces of the yarn 2A, 2B, and the Si—SiC-basedmaterial phase that has grown in the silicon carbide phase 5C separatedfrom the yarn.

[0054] Each of the Si—SiC-based material phase, preferably, has aninclined composition in which the silicon concentration becomes loweraccording to the distance from the surface of the yarn, or preferably,comprises a silicon phase.

[0055] As shown in FIG. 5(a), the fiber-composite material 11 accordingto the present invention, preferably, comprises the C/C composite 15 andthe fiber-composite material layer 13 that has grown by that the surfaceof the C/C composite 15 is impregnated with Si, and the silicon layer 14may have grown on the fiber-composite material layer 13. Referencenumeral 12 shows the area of the body of C/C composite that has neverbeen impregnated with Si. As shown in FIG. 5(b), the whole of theelement 16 is preferably formed with the fiber-composite materialaccording to the present invention.

[0056] In the case that the fiber-composite material layer 13 isprovided, the thickness thereof is preferably 0.01 to 1 mm. Further, theSi concentration in the fiber-composite material layer preferablybecomes higher from the surface of a carbon fiber toward the outside.

[0057] If the fiber-composite material according to the presentinvention contains 10 to 70% by weight of carbon fiber, the material maycontain, for example, the elements other than carbon such as boronnitride, boron, copper, bismuth, titanium, chromium, tungsten andmolybdenum.

[0058] The thickness of the fiber-composite material layer 13, that isprovided by the fact that Si—SiC is impregnated into the body material,is described in more detail.

[0059] With regard to the relations with a carbon fiber bundle 3, asilicon carbide phase 4B, and a silicon phase 5B; the C/C composite 15,the layer 13, and the silicon layer 14 correspond to the carbon fiberbundle 3, the silicon carbide phase 4B, and the silicon phase 5B,respectively, in FIG. 2(a).

[0060] Here, the layer 13 has a thickness of preferably 0.01 to 1 mm,more preferably 0.05 to 1 mm.

[0061] At this time, the layer 13 is preferably formed in such a waythat the Si concentration inclines in a range of from 0/90 to 90/100from a portion of the carbon fiber bundle 3 toward a portion of thesilicon phase 5B through the silicon carbide phase 4B.

[0062] Inclination of Si concentration is hereinbelow described indetail by taking a macroscopic view on a supposition of a block having athickness of 200 mm.

[0063] In the present invention, since a laminate of carbon fiberbundles is impregnated with Si, the center of the block having athickness of 200 mm has the lower Si concentration, and a portion aroundthe surface layer has the higher Si concentration. Because of this, themost preferable mode can be realized by forming a molded or sinteredbody of a C/C composite so that the porosity becomes lower from thesurface toward the incide and by disposing and forming a plurality ofpreformed sheets made of preformed yarn which has various binder pitchesso that the binder pitch becomes higher from the inside toward thesurface. In the case of FIG. 2(a), SiC concentration (=Si concentration)becomes lower in the order of “silicon carbide phase 4A of yarn arrayelements 1A layer”>“silicon carbide phase 4A of yarn array elements 1Blayer”>“silicon carbide phase 4A of yarn array elements 1Clayer”>“silicon carbide phase 4A of yarn array elements 1D. Therefore,Si concentration inclines in a maximum thickness of about 100 mm in amacroscopic view. The Si concentration preferably inclines in a range offrom 90/100 to 0/100 from the surface toward the inside of the layer 13.

[0064] The fiber-composite material according to the present invention,as described above, may contain one or two or more than two substancesselected from the group consisting of boron nitride, boron, copper,bismuth, titanium, chromium, tungsten and molybdenum.

[0065] Because these substances have a lubricant property, byimpregnating these substances into the body material made of C/Ccomposite, even in the part of the body material impregnated withSi—SiC-based material, the lubricant property of fiber can be maintainedand the decline of physical properties can be prevented.

[0066] For example, the boron nitride content is preferably 0.1 to 40%by weight to 100% by weight of the body material made of C/C composite.It is because the effect of addition of lubricant property with boronnitride cannot be adequately obtained in the concentration that is lessthan 0.1% by weight, and, in the case in which the concentration that ismore than 40% by weight, the brittleness of boron nitride appears in thecomposite material.

[0067] The fiber-composite material according to the present inventioncan be produced preferably in the following process.

[0068] Carbon fiber bundles are made by making the bundles containpowdery binder-pitch and cokes that eventually become a matrix, and,further, if necessary, by making the bundles contain phenol resinpowder. A soft coat made from plastic such as thermal-plastic resin ismade around the carbon fiber bundle to obtain a soft intermediatematerial. The soft intermediate material is made to have a yarn-shape(Japanese Patent Application Laid-Open No. 2-80639), and is molded witha hot press at 300 to 2000° C. at atmospheric pressure to 500 kg/cm² toobtain a molded product after the necessary amount of the material islaminated. According to the demand, the molded product is carbonized at700 to 1200° C., and is made to be graphite at 1500 to 3000° C. toobtain a burned product.

[0069] The carbon fiber may be any one of the pitch-based carbon fiberthat is obtained by providing pitch for spinning use, melt-spinning thepitch, making the pitch infusible and carbonizing the pitch, and PNAbased carbon fiber that is obtained by giving flame resistance toacrylonitrile polymer (or copolymer) fiber and by carbonizing the fiber.

[0070] As an organic binder that is necessary for making a matrix,thermosetting resins such as phenol resins and epoxy resins, tar andpitch may be used, and these may contain cokes, metal, metal compounds,inorganic and organic compounds. A part of the organic binder sometimesbecomes a source of carbon.

[0071] After that, this molded product or this burned product, producedas in the above method, and Si are held in a temperature range of 1100to 1400° C. under a pressure of 0.1 to 10 hPa in the furnace for one ormore than one hour. Preferably, in the process, inert gas is allowed toflow to form Si—SiC layer on the surface of the molded product or theburned product, in such a way that 0.1 or more than 0.1 (NL)(normallitter: corresponding to 5065 litter at 1200° C., under a pressure of0.1 hPa) of the gas is allowed to flow per 1 kg of the total weight ofthe molded product, or the burned product, and Si. Thereafter, thetemperature is raised to 1450 to 2500° C., preferably, to 1700 to 1800°C. to melt Si—SiC-based material, to impregnate the material into theinside of the pores of the above-described molded product or the burnedproduct, and to form the material. In the process, in the case in whichthe molded product is used, the molded product is burned to obtain thefiber-composite material.

[0072] The molded product, or the burned product, and Si are held at atemperature of 1100 to 1400° C., under a pressure of 1 to 10 hPa for onehour or more. In the process, the amount of inert gas to be used iscontrolled in such a way that per 1 kg of the total weight of the moldedproduct, or the burned product, and Si, 0.1 or more than 0.1 NL,preferably, 1 or more than 1 NL, more preferably, more than 10 NL ofinert gas is made to flow.

[0073] Thus, in the burning process (namely, in the process in which Siis not yet melted or impregnated), because providing an atmosphere ofinert gas removes the generated gas such as CO brought by the change inwhich inorganic polymer or inorganic substance become ceramics from theatmosphere of burning and prevents the contamination of the burningatmosphere caused by the outside factor such as O₂ or the like in theair, it is possible to keep low porosity of the fiber-composite materialthat is obtained by melting and impregnating Si in the subsequentprocess.

[0074] In the process in which Si is melted and impregnated into themolded product or the burned product, the surrounding temperature israised to 1450 to 2500° C., more preferably to 1700 to 1800° C. Then,the pressure in the burning furnace is maintained preferably in a rageof 0.1 to 10 hPa. The atmosphere in the furnace is preferably an inertgas or argon gas atmosphere.

[0075] As described above, because the combination of the usage of thesoft intermediate material, the impregnation of silicon and the fusionof silicon brings about the retention of long and narrow pores betweenthe yarn in the burned product or the molded product, silicon migratesinto the inner part of the molded product or the burned product alongthe long and narrow pores. In the migration process, silicon reacts withcarbon in the yarn and is gradually carbonized from the surface side ofthe yarn to produce the fiber-composite material according to thepresent invention.

[0076] The inclination of concentration in Si—SiC-based material in thewhole fiber-composite material layer is controlled with the porosity andthe diameter of the pores of the compact or the sintered body. Forexample, in the case where the concentration of Si—SiC-based materiallayer is made higher than any other portion at a depth of 0.01 to 10 mmfrom the surface layer of the fiber-composite material, the porosity inthe portion having a desired high concentration in the compact or thesintered body is made to be in the range from 5 to 50% and the averagediameter of the pores is made to be 1 μm or more. In the other portions,the porosity and the average diameter of the pores is made the same orlower than the portion having the high concentration. The porosity inthe portion having the desired high concentration of the compact orsintered body is preferably 10-50% and the average diameter of the poresis preferably 10 μm or more. It is because the binder in the compact orthe sintered body is hard to be removed if the porosity is less than 5%,and impregnation of the portion except for the portion having thedesired high concentration with the Si—SiC-based material proceedsbeyond the range of control of an amount of Si and other parameters of aproduction method such as a contact time.

[0077] In order to form the fiber-composite material layer on thesurface of C/C composite, the molded product designed to have a porosityof 0.1 to 30% at least in the part near to the surface during burning ispreferably used.

[0078] In order to make the porosity in the molded product or the burnedproduct become lower from the surface toward the inside, more than onepreformed sheets, made of preformed yarn of different binder-pitch, arearranged and molded in such a way that from the inside to the surfacelayer side the binder-pitch becomes larger.

[0079] In order to make the silicon concentration in the fiber-compositematerial layer have an incline, the burned product adjusted to have theporosity in the part near to the surfaces which becomes lower from thesurface to the inside, or the molded product adjusted to have theporosity at least in the part near to the surface which becomes lower,during burning, from the surface to the inside are used to produce thefiber-composite material.

[0080] Characteristics and effects of a fiber composite material of thepresent invention are hereinbelow described.

[0081] (1) Since a fiber composite material of the present invention hasa matrix containing a Si phase, its porosity can be controlled to belower. If all Si reacts with C to produce SiC, pores corresponding to adifference of specific gravity are generated because specific gravitiesof Si, C, and SiC are 2, 2, and 3.2, relatively. Since the compositematerial of the present invention has a low porosity, it has a smallsurface area, and a combustion probability owing to an oxygen attack islowered. Therefore, antioxidation ability of the composite material canbe maintained in comparison with a material having a high porosity.

[0082] A fiber composite material of the present invention has aporosity of preferably 0.5-5%, more preferably 1-3%. When the porosityexceeds 5%, its antioxidation ability cannot be maintained. Further,large pores or many pores are present. Therefore, when the compositematerial is used as a sliding material, it increases possibility thatmuch of the other sliding material is scraped and kept inside the poresduring sliding and that the composite material, which is a slidingmaterial, breaks.

[0083] When the porosity is lower than 0.5%, the following phenomenon,which happens in a conventional SiC—C/C composite material, is prone togenerate partially.

[0084] (2) Further, in the case of a conventional SiC—C/C compositematerial, a porosity had to be increased so as to completely leavefibers or uniformly disperse fibers and SiC wholly.

[0085] The reason is as follows: Si is reacted with C at a highertemperature in order to completely fill the pores. Further, paths forpermeating Si of a C/C substrate to be impregnated are uneven. Thishinders a smooth flow of Si. Therefore, a reaction producing SiCcompletely proceeds in portions where the paths are clogged with Si, andfibers in the portions are destroyed. On the other hand, the reactionproducing SiC proceeds very little in a periphery of fibers in portionswhere Si does not reach. Thus, the conventional composite materialbecomes very uneven on the whole.

[0086] On the contrary, a composite material of the present invention, aflow path for permeating Si into the C/C substrate is very uniformlyformed three-dimensionally. Therefore, the composite material is freefrom the problems of partially having a strong reaction producing SiC orinsufficiently having the reaction producing SiC. Thus, a homogeneousthree-dimensional composite material can be obtained.

[0087] (3) Further, a fiber composite material of the present inventionhas a self-repairability by Si which remains with an inclination of aconcentration besides SiC and C/C composite.

[0088] A material containing only SiC and C/C composite causes a strainbetween C and SiC during heating because their thermal expansioncoefficients are different from each other, thereby forming a crack. Thecrack is never repaired.

[0089] On the other hand, in the case of a fiber composite material ofthe present invention, Si is present on the outer surface of SiC asdescribed above. Therefore, self-repairing can be conducted by apenetration of molten Si into a crack, or self-glazing can be conductedby generation of SiO₂ by Si oxidation. That is, the material hasself-repairability.

[0090] (4) Further, in a fiber composite material of the presentinvention, which contains Si, a thermal resistance or an electricresistance is prone to be changed more greatly when the material isreduced by excessive abrasion. Therefore, the material can exhibit afunction of a sensor. Additionally, when a temperature of Si risesunusually in a high vacuum, Si evaporates at about 1400° C., which issufficiently lower than 2700° C., at which SiC is sublimated. Therefore,a sensing function that can give warning of an extraordinary state byconfirming a change of weight or by changing of electrical, thermalproperties can be exhibited.

[0091] Hereinafter, the present invention is illustrated in more detailby examples, however, the present invention is not limited to theexamples.

[0092] The properties of the composite materials obtained by eachexample are measured by the methods as described below.

[0093] (Method of Measuring Porosity)

porosity (%)=[(W 3−W 1)/(W 3−W 2)]×100

[0094] (by Archimedês method)

[0095] Dry weight (W1): measured after drying the sample at 100° C. for1 hour in an oven.

[0096] Under water weight (W2): measured in water after boiling thesample in water and making water migrate into the pores completely.

[0097] Drinking weight (W3): measured at atmospheric pressure aftermaking water migrate into the sample completely.

[0098] (Method of Evaluating Oxidation Resistance)

[0099] The oxidation resistance is measured by measuring the loss rateof weight, after 200 hours, of the sample cut out as a test piece of 60mm×60 mm×5 mm (thickness), held for 200 hours at 1150° C. in a furnace(1%O₂, 99%N₂).

[0100] (Method of Evaluating Compressive Strength)

[0101] Compressive strength is calculated using the compression-loadedtest piece with the following formula.

Compressive strength=P/A

[0102] (in the formula, P is the load when loaded with the maximum load,A is the minimum sectional area of the test piece.)

[0103] (Method of Evaluating Durability Under Oxidative Condition atHigh Temperature)

[0104] The weight of the cut out test piece, is measured, of 60 mm×60mm×5 mm (thickness), held at 1200° C. using a mixed gas of 99% of Ar and1% of O₂.

[0105] (Method of Evaluating Interlaminar Shear Strength)

[0106] Interlaminar shear strength is calculated with the followingformula, after three-point bending, regarding the distance of the testpiece thickness h multiplied by 4 as the distance between the supports.

Interlaminar shear strength=3 P/4bH

[0107] (In the formula, P is the maximum bending load when broken, and bis the width of the test piece)

[0108] (Method of Evaluating Bending Modulus)

[0109] Bending modulus is calculated with the following formula, usingthe initial gradient P/σ of the straight part of load-deflection curve,after three-point bending, regarding the distance of the test piecethickness h multiplied by 40 as the distance between the supports.

Bending modulus=1/4·L ³ /bh ³ ·P/σ

[0110] (in the formula, b is the width of the test piece)

[0111] (Method of Evaluating Self-Restoration)

[0112] Self-restoration is measured on the test piece annealed for 2hours at 900° C., after making micro-cracking inside by applyingrepeated stresses of Max: 20 Mpa to Min: 5 Mpa, 100,000 times.

[0113] (Method of Evaluating Dynamic Coefficient of Friction)

[0114] The frictional force Fs(N) is measured on the test piece of 60mm×60 mm×5 mm (thickness) mounted on a rotary jig and pressed againstthe partner material (SUJ, 10 mm ball) with a constant load Fp(N).

[0115] The dynamic coefficient of friction is calculated with thefollowing formula.

Coefficient of friction μ=Fs/Fp

[0116] (Method of Evaluating Specific Abrasive Wear)

[0117] The weight untreated, Wa (mg) and the weight treated, Wb (mg) aremeasured on the test piece, size of which is 60 mm×60 mm×5 mm(thickness), mounted on a rotary jig and pressed against the partnermaterial (SUJ, 10 mm ball) with a constant load P. Abrasive wear V (mm³)is calculated with the following formula, using the density ρ (g/cm³) ofthe test piece.

V=(Wa ρ Wb)/ρ

[0118] Specific abrasive wear Vs (mm³/(N·km)) is calculated with thefollowing formula, using abrasive wear V (mm³), test load P (N) andsliding distance L (km).

Vs=V/(P·L)

EXAMPLE 1

[0119] By impregnating phenol resin to carbon fibers pulled and alignedin one direction, about ten thousand carbon long fibers of diameter 10μm were tied in a bundle to obtain a fibrous bundle (yarn). The yarn wasarranged as shown in FIG. 1 to obtain a prepreg sheet.

[0120] Then, the prepreg sheet was laminated so as to have 50 layers andprocessed at 180° C. and at 10 kg/cm² with a hot press to cure thephenol resin and was burned at 2000° C. in nitrogen to obtain a c/ccomposite. The obtained c/c composite had a density of 1.0 g/cm³ and aporosity of 50%.

[0121] The c/c composite was then vertically placed in a carbon cruciblefilled with silicon powder of purity 99.8% and of mean particle size 1mm. After that, the crucible was moved into a burning furnace. The c/ccomposite was processed to impregnate silicon into the composite andproduce the fiber-composite material according the present invention,under the following condition: the burning furnace temperature of 1300°C., the flow rate of argon gas as inert gas of 20 NL/minute, the furnaceinternal pressure of 1 hPa, the holding time of 4 hours and then thefurnace temperature was raised to 1600° C. while the same furnacepressure was kept. In this Example, the whole c/c composite was changedto the fiber-composite material of the present invention.

[0122] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1.

[0123] Each of the data were measured on the test piece cut from thenear part of the surface layer in which Si—SiC type material and C/Ccomposite were adequately combined.

[0124]FIG. 6 is a photograph of EPMA (electron beam micro analyzer) thatshows the constitution of a ceramic material in the sectional directionto the surface layer of the test piece. FIG. 7 is a photograph ofreflective electronic image by SEM showing the constitution of the sameceramic material. FIG. 8 is a schematic cross sectional view based onFIG. 6 and FIG. 7 showing the microstructure at the boundary areabetween the yarn.

[0125] The photographs of FIG. 6 and FIG. 7 show that Si and C have amicro- and fixed concentration gradient of about 0.01 to 0.1 mm scale.That is, as shown in FIG. 8, silicon-carbide phase 5C has grown alongthe surface of yarn 2B on the side near the surface of yarn 2B amongmatrix 8B and silicon phase 4C has grown inside the phase 5C. It isbecause the constitutional difference between the phases 4C and 5C canbe observed from FIG. 7 and, as in FIG. 6, both of carbon and siliconexist in the phase 5C, but carbon is not observed in phase 4C.

EXAMPLE 2

[0126] The C/C composite produced in the same way as Example 1 wasimpregnated with phenol resin and was burned at 2000° C. in nitrogenafter the resin was cured at 180° C. in an oven under normal pressure.By repeating the process further five times, a C/C composite wasobtained. The obtained C/C composite had density of 1.4 g/cm³ andporosity of 30%.

[0127] After that, the obtained C/C composite was impregnated with Si inthe same way as Example 1 to produce a fiber-composite material.

[0128] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material were shown in Table 1. Each of the data weremeasured on the test piece cut from the near part of the surface layerof the fiber-composite material in which Si—SiC type material and C/Ccomposite were adequately combined.

EXAMPLE 3

[0129] A fiber-composite material comprising fiber-composite-materiallayers were produced.

[0130] A C/C composite was produced in the following process.

[0131] Preformed yarn was produced by preformed yarn method (JapanesePatent Application Laid-Open No. 2-80639). One-direction-preformed-yarnsheets were produced using the preformed yarn. The sheets were laminatedin such a way that the carbon fibers were intersected at right angleseach other, and were molded at 600° C. and at 100 kg/cm² with a hotpress. The obtained C/C composite had density of 1.8 g/cm³ and porosityof 10%.

[0132] The obtained C/C composite was impregnated with Si in the sameway as Example 1 to produce a fiber-composite material. Thefiber-composite material layer had a thickness of 10 mm.

[0133] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material were shown in Table 1. Each of the data weremeasured on the test piece cut from the near part of the surface layerof the fiber-composite material in which Si—SiC type material and C/Ccomposite were adequately combined.

EXAMPLE 4

[0134] A fiber-composite material comprising fiber-composite-materiallayers were produced in the same way as Example 1. However, boronnitride was added in the process of producing C/C composite so thatboron nitride is contained in the fiber-composite-material layers. Thefiber-composite-material layer was designed to have a thickness of 30mm.

[0135] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material were shown in Table 1. Each of the data weremeasured on the test piece cut from the near part of the surface layerof the fiber-composite-material in which Si—SiC type material and C/Ccomposite were adequately combined.

EXAMPLE 5

[0136] A fiber-composite material comprising fiber-composite-materiallayers were produced in the same way as Example 1. In this Example 5, Siconcentration in fiber-composite-material layer was designed to have agradient in such a way that the concentration becomes low from thesurface to the inside. The fiber-composite-material layer was planned tohave a thickness of 3 mm. The concentration gradient of Si was designedto incline in a range of 100/0 to 0/100 compared with the amount ofcarbon fiber from the surface to the inside of thefiber-composite-material layer.

[0137] A C/C composite was produced by the following method.

[0138] Ten types of preformed yarn were produced at the rate of thebinder pitch in the preformed yarn of 20 to 60 by preformed-yarn method.One-direction preformed sheets were produced using this preformed yarn.The preformed sheet having the binder pitch rate of 20 was placed in thecenter of the thickness, the preformed sheet was placed in order in sucha manner that the binder rate becomes high toward the surface layer, andthe preformed sheet having the binder pitch rate of 60 was placed in thenearest side to the surface. Then, these preformed sheets were laminatedin such a way that the carbon fibers were intersected at right angleseach other, and were molded at 600° C. and at 100 kg/cm² with a hotpress. After that, these preformed sheets were burned at 2000° C. innitrogen to obtain a C/C composite. The obtained C/C composite haddensity of 1.6 g/cm³ and porosity of 10%.

[0139] The obtained C/C composite was impregnated with Si in the sameway as Example 1 to produce a fiber-composite material.

[0140] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. Each of the data weremeasured on the test piece cut from the near part of the surface layerof the fiber-composite material in which Si—SiC type material and C/Ccomposite were adequately combined.

COMPARATIVE EXAMPLE 1

[0141] A C/C composite was produced in the same way as Example 3.

[0142] The measured results such as density, porosity, shearing strengthamong layers, compression strength and bending modulus of the obtainedfiber-composite material are shown in Table 1. TABLE 1 Porosity Compres-Bending Interlaminar Specific Dynamic Density of of body sive mod- shearabrasive coefficient Oxidation body material material Density Porositystrength ulus strength wear (mm³/ of friction Self- resistance (g/cm³)(%) (g/cm³) (%) (Mpa) (Gpa) (Mpa) (N · km) (μ) restoration (%) Example 11.0 50 2.2 1 to 2 190 40 22 0.0 0.55 140/190 4 2 1.4 30 2.1 1 to 2 18045 20 0.0 0.18 120/180 6 3 1.8 10 2.0 1 170 48 18 0.0 0.05 100/170 10 41.4 50 2.1 1 to 2 200 55 23 0.0 0.26 115/200 6 5 1.6 50 to 10 2.1 1 to 2190 45 20 0.0 0.21 130/190 4 Comparative 1 1.8 10 — — 140 50 16 0.550.05 0 (none)/ 100 Example 150

[0143] Table 1 suggests that the fiber-composite materials (Examples 1to 5) according to the present invention show good results incompression strength and in shearing strength compared with C/Ccomposite (Comparative Example 1), and that the fiber-compositematerials show almost the same result in bending modulus compared withC/C composite. In the fiber-composite materials according to the presentinvention, impregnating Si—SiC type material into C/C composite makesC/C composite become stronger in compression strength than C/Ccomposite. It is thought that it is because the Si—SiC type materialcomes among carbon fibers.

[0144] The fiber-composite material into the layer of which is addedwith boron nitride (Example 4) showed a better result in bending modulusthan other examples. Moreover, the fiber-composite material with thegradient of Si concentration in fiber-composite material layers (Example5) showed better result in self-restoration than other Examples.

INDUSTRIAL APPLICABILITY

[0145] As described above, because the fiber-composite materialaccording to the present invention has configuration in whichfundamental structure is composed of body material made of c/c compositeand the body material is impregnated with Si—SiC, the fiber-compositematerial has high-impact properties, lightweight properties and highstrength properties, which are characteristics of c/c composite, andhigh oxidation resistance, high creep resistance and spallingresistance, which are not characteristics of c/c composite.

[0146] Further, in the fiber-composite material according to the presentinvention, making Si concentration in the fiber-composite material layerhave an inclination in such a way that the concentration becomes lowfrom the surface to the inside can remarkably improve corrosionresistance and strength in oxidation and corrosion environments, andhealing function to the defects in the surface and subsurface parts.

[0147] In the fiber-composite material according to the presentinvention, making the fiber-composite material layer comprise boronnitride can prevent toughness deterioration of c/c composite portion bybeing impregnated with Si—SiC-based material.

1. A fiber-composite material comprising: a yarn aggregate in which yarnincluding at least a bundle of carbon fiber and a carbon component otherthan carbon fiber is three-dimensionally combined and integrally formedwithout separation from each other; and a matrix made of Si—SiC-basedmaterial filled between the yarn adjacent to each other within the yarnaggregate.
 2. A fiber-composite material as claimed in claim 1, whereinthe matrix has a silicon carbide phase having grown along the surface ofthe yarn.
 3. A fiber-composite material as claimed in claim 2, whereinthe matrix has a silicon phase comprising silicon, the silicon carbidephase has grown between the silicon phase and the yarn.
 4. Afiber-composite material as claimed in any one of claims 1 to 3, whereinthe matrix has an inclined composition in which the content rate ofsilicon becomes higher as apart from the surface of the yarn as far. 5.A fiber-composite material as claimed in any one of claims 1 to 4,wherein the yarn aggregate includes a plurality of yarn array elements,each of the yarn array elements is formed by arranging the plurality ofyarn in a substantially parallel direction and two-dimensionally, andeach of the yarn array elements is laminated to form the yarn aggregate.6. A fiber-composite material as claimed in claim 5, wherein the yarnarray elements adjacent to each other have a structure in which thelongitudinal direction of each yarn intersects with each other.
 7. Afiber-composite material as claimed in any one of claims 1 to 6, whereinthe matrices are connected to each other within the fiber-compositematerial to form a three-dimensional network structure.
 8. Afiber-composite material as claimed in claim 6, wherein the matrices arearranged in a substantially parallel direction and two-dimensionallywithin each of the yarn array elements, and the matrices having grownwithin each of the yarn array elements adjacent to each other areconnected to each other, to thereby form a three-dimensional lattice ofthe matrices.
 9. A method of preparing fiber-composite material,comprising the steps of: producing bundles of carbon fiber byimpregnating a component of powdery carbon into the bundles of carbonfiber, which eventually forms a matrix shape; forming a plastic coataround the bundles of carbon fiber to obtain an intermediate material;molding the intermediate material to obtain a molded product by makingthe intermediate material into a yarn-shape and laminating apredetermined amount of the material, or burning the molded product toobtain a burned product; holding the molded product or the burnedproduct and Si, at 1100 to 1400° C. in an atmosphere of inert gas; andheating the molded product or the burned product and Si to a temperaturefrom 1450 to 2500° C., to thereby impregnate Si—SiC-based material intothe inside of pores of the molded product or the burned product.
 10. Amethod of preparing fiber-composite material as claimed in claim 9,wherein the molded product or the burned product and Si are held at atemperature of from 1100 to 1400° C. under a pressure of 0.1 to 10 hPafor one or more hours, and an inert gas is controlled to flow in anamount of 0.1 or more normal litters (NL) of per 1 kg of the totalweight of the molded product or the burned product.
 11. A method ofpreparing fiber-composite material as claimed in claims 9 or 10, whereinthe molded product or the burned product and Si are heated to atemperature of from 1450 to 2500° C. under a pressure of 0.1 to 10 hPa.